Natural Course of Myofascial Trigger Points

Only one longitudinal study is known that examined the muscles for
taut bands and for evidence of TrP tenderness in a normal population to
learn the incidence of TrPs. Fricton,et a1.(45) examined 269 female
nursing students initially, again at 18 months and at 36 months for
evidence of masticatory myofascial pain attributable to TrPs. They found
an annual incidence of 8% with 5% developing masticatory myofascial
pain only, and with 3% developing mixed myofascial pain and disk
displacement in the temporomandibular joint. Additional studies will
give us a more complete picture of what the natural course of myofascial
TrPs may be. Figure 1 outlines a proposed natural course of myofascial
pain caused by TrPs, based on information now available. The common
presence of taut bands in pain-free individuals (12,42) suggests that
taut bands are a necessary precursor to the development of TrPs. Some
individuals appear to be genetically more vulnerable to the development
of taut bands than others. Apparently, because of stressful life events
and abnormal muscle stress (46) combined with genetic predisposition, a
latent TrP develops in a taut band. This TrP, with further mechanical
stress or other aggravating [perpetuating factors, can develop into an
active TrP. The active TrP may recover spontaneously, may persist
without progression, or, in the presence of perpetuating factors, the
individual may develop additional TrPs and a chronic myofascial pain
syndrome. Although in the past it had been assumed that TrPs caused a
taut band (31,35), it now appears more likely that a taut band is a
necessary precursor to the development of a TrP. In one study (12) taut
bands were found to occur with nearly equal frequency in control
subjects, myofascial pain patients, and FM patients. This indicates that
neither myofascial pain nor FM significantly influences the number of
taut bands present. A more recent study (42) reported that both
examiners [100% agreement] found taut bands present in 6 of 63 [nearly
10%] of normal control subjects. These bands were the only suggestion of
TrPs found in these normal subjects, who were free of spot tenderness.
In 1989, Pellegrino, et a1.(47) reported clinical signs and symptoms
that they identified as primary FM, but the description fit a diagnosis
of myofascial TrPs much better than it fit FM (48). They described
"abnormal, palpable muscle consistency years before acquiring clinical
symptoms in teenage twins" (47). There are no studies which indicate
that palpable bands are a diagnostic criterion for tender points of FM,
but there is much clinical experience (31) and experimental evidence
(49,50) that taut bands are an integral part of the TrP phenomenon. This
study of 17 families (47) suggests that a proclivity to develop taut
bands is an inherited characteristic and that those who are more prone
to develop taut bands are also more likely to develop TrPs. In addition
to general agreement among clinicians (2,4,7,8), the only documented
evidence that muscle overload can initiate TrPs or convert a latent TrP
into an active one is the study by Fricton, et a1.(46). Specifically,
the course of an untreated latent TrP has not been studied. An incidence
study of masticatory myofascial pain suggests that a latent TrP
probably persists, with occasional increase in activity sufficient to
cause symptoms become an active TrP]. An active TrP sometimes regresses
without treatment to a latent TrP (45). Latent TrPs have been known to
persist for many years, painlessly restricting range of motion, and then
respond immediately to spray-and-stretch therapy. After an individual
develops an active TrP, especially in the absence of any perpetuating
factor, continuing normal gentle daily activity and avoiding muscle
overload often permit spontaneous regression from an active TrP to a
latent one in a few days to a few weeks. The presence of perpetuating
factors assures persistence of an active TrP and sets the stage for the
development of secondary TrPs, additional symptoms, and chronicity with
progressive functional disability and psychological distress (31,34).
The presence of perpetuating factors is one of the most common, and
often one of the most important, factors in the management of patients
with chronic myofascial TrPs (6,8,34). Recently, Gerwin demonstrated
that iron insufficiency is a risk factor for myofascial pain caused by
TrPs (51).